There are many types of roofing systems used with various types of buildings. For larger buildings with generally flat roofs, a roofing system employing flexible sheet material, for an example EPDM rubber sheeting or membrane, as the upper surface is becoming increasingly popular due to its many advantages. These membranes are generally secured to the roof in four manners, ballast, adhesion, penetrating fasteners and non-penetrating fasteners. Ballast can shift in high winds and is not suitable by itself. Adhering the membrane to the roof is extremely expensive. Penetrating fasteners create holes through the membrane which must be sealed and increase the likelihood of leakage. Non-penetrating mechanical fasteners are inexpensive and do not create holes through the membrane. For these reasons the non-penetrating fasteners are gaining in popularity.
One particular non-penetrating mechanical fastening system is disclosed in German Patentschrift No. 2,804,962 and a modified version of this disclosed in U.S. Pat. No. 4,519,175, the disclosure of which is incorporated herein by reference. With this system the membrane is held to anchoring discs fastened to the roof. Anchoring discs which includes raised, hollow, inverted frusto-conical buttons are screwed or nailed to the roof. The roof membrane is laid over the roof and over these anchoring discs. An externally threaded tined retainer cap is then forced over the buttons with the membrane held therebetween. The tines of the retainer caps deflect outwardly to permit them to fit over the button and membrane. An internally threaded cover screws onto the externally threaded retainer cap with the lower ends of the tines projecting into the region below the upper section of the button, holding the tines in place and preventing the retainer cap from popping off. Thus, the membrane is anchored to the roof without puncturing the membrane.
There are several potential disadvantages with this particular fastener. As the cover is screwed onto the retainer, the retainer cap may rotate with the cover as it is being screwed down. This rotation of the retainer cap would unduly stress the membrane increasing the likelihood of ripping the membrane.
Further, the internal diameter of the retainer cap is smaller than the external surface of the upper rim of the button. The tines are required to flex outwardly to a large degree during installation in order to permit it to fit over the button and the membrane. If done improperly this causes the tines to scrape the membrane as the retainer cap is placed over the membrane and button in some cases, tending to rip the membrane. Also the top rim of the button in the past has been flat. When the retainer cap is pushed over the button it engages the membrane at the top rim and stresses the membrane as it is forced over the button.
Further, as the retainer cap is forced over the membrane the individual tines are free to move upwardly. Different tines may move upwardly to different extents such that threads on adjacent tines are not aligned. The external threads on the tines being out of alignment prevent or hinder screwing the cover over the retainer cap.
These fasteners are basically three piece fasteners with the anchoring disc fixed to the roof substrate and the membrane placed over the anchoring disc. The retainer cap is then placed over the membrane and the anchoring disc and finally the cover is placed on and screwed onto this retainer cap. This is a relatively inconvenient method of securing a membrane to a roof which requires several pieces to be assembled at the building site.